This invention generally relates to a method and apparatus for detecting cardiac depolarizations for remote monitoring of electrocardiograms (ECGs) from patients with an implanted medical device (IMD). More particularly, this invention pertains to hand-held electrodes for recording and transmitting ECG data to a remote site for analysis by a physician, clinician, or diagnostician.
Cardiac muscle is an excitable tissue and includes electrically excitable cardiac muscle cells. Typically, upon intrinsic or artificial supra-threshold electrical excitation, cardiac muscle cells generate a depolarization wave that triggers a delayed contraction. Cardiac muscle cells are electrically coupled enabling the flow of depolarization waves between them. Normally, a group of pacemaker cells located at the Sino-Atrial node in the right atrium originates the depolarization wave that then spreads rapidly to the rest of the heart, first to the atria and then to the ventricles. An ECG is the record of the cardiac depolarizations. A physician uses ECGs to determine a patient""s cardiac conduction condition. Depending on the patient""s medical condition, it may be needed to document the patient""s status at times other than the patient""s clinic visit or hospital stay. Typically and prior to the advent of remote monitoring capability, an ECG reading is taken only in a clinical or hospital environment.
Since a patient""s skin exhibits voltage differences due to electrical depolarizations of the heart""s muscle cells, ECG signal acquisition involves the use of two or more electrodes placed on a patient""s skin. In a clinic, ECGs are recorded via a number of sensing electrodes. An individual electrode usually includes a metal contact that attaches to the patient""s skin with an adhesive bandage on which a conductive gel is placed. When paired with other electrode(s), electrode pairs detect changes in electrical potential across the patient""s skin. These signals represent cardiac depolarizations and are fed to a recorder that may store them or print them out on a roll of paper as ECG tracings. The ECG electrodes are also capable of detecting artifacts from IMDs such as those indicating a pacing output pulse and printing these on the resultant tracing.
As the technology associated with IMDs advanced, it soon became clear that it was necessary to have a remote ECG monitoring capability. Transtelephonic ECG monitoring soon became routine for patients with IMDs. Typically, such monitoring is short-term, and involves the patient contacting the physician by phone, and employing an ECG transmitter of the type described in U.S. Pat. No. 4,151,513, issued to Menken et al. Use of such a device, however, typically requires the patient to apply ECG electrodes to the body, and subsequently to couple the monitoring device to their telephone to allow for a brief period of monitoring.
Alternatively, U.S. Pat. No. 5,503,158 issued to Cuppock, et al describes an ambulatory ECG monitor with a number of sensors placed on the patient""s skin to generate an ECG. An amplifier is connected to the sensors to generate an amplified signal. A remote processor is equipped with a receiver and is connected to the amplifier to receive and process the amplified signal to obtain the patient""s electrocardiogram.
Other methods have also been described, for example, attaching electrodes to the wrist in U.S. Pat No. 5,289,824, issued to Mills et al, or one of the fingers of each hand. In the ""824 patent, incorporated herein by reference in its entirety, a wrist-worn monitor is provided that, without external connections of any kind, enables local, multiple event ECG data recording and telecommunication to a remote site. The monitor is housed in a compact and lightweight housing and is operable whenever the patient simply places his/her hand over a portion of the monitor""s face to contact an upper skin electrode. Circuitry is provided to drive an integral speaker for the telecommunication of the ECG signal or cardiac event data via telephone lines to a remote site for so-called xe2x80x9cover-readxe2x80x9d, diagnosis and archival recording. The monitor""s housing includes dual, integral dry skin electrodes located on a wrist contacting, inner or rear base plate and on an outer or front surface contactable by the palm of the patient""s other hand.
Because the average age of the patients who receive an IMD is generally over seventy, the application and use of ECG electrodes often poses various operational and implementation issues. For example, in the ""158 patent, multiple electrodes are placed on the patient""s upper torso and remain there over a period of time. These attached electrodes may irritate the skin and make it difficult to take a shower. The wrist electrode, described is the ""824 patent, eliminates the permanent application of electrodes while maintaining the ability to have a connection to a remote monitor as disclosed in the ""158 patent. The wrist electrode, however, is not without its own problems. For example, an elderly patient may have arthritis and find it quite difficult to attach wrist electrodes or, due to very thin wrists, keep them in close contact with the skin.
Other types of electrodes, especially those intended for direct application to the skin, such as stick-on electrodes that require a conductive gel, are quite difficult for any patient to apply regardless of his or her age. Removing these types of electrodes can cause extreme skin irritation to a patient of any age, but especially to an elderly patient whose skin may likely be quite thin. Finally, positioning such electrodes requires training in order to acquire an adequate signal that result in an ECG of diagnostic quality.
Transtelephonic systems, known in the art, seem to require a number of connecting cables to attach the sensing electrodes to the monitoring device. The number of cables may increase when a separate RF head is provided to detect and transmit simultaneous data from the IMD. The responsibility to ensure an adequate connection of these cables to the monitor should not be left to patients. This is partly because patients may forget and, in most cases, may not be comfortable operating electronic equipment.
Accordingly, current patient management and follow-up require a nurse, clinician/technician call or inform the patient of the need for an ECG tracing when, for example, a physician may ask for one. This call may serve as a reminder to the patient that the appointment is scheduled for some time in the future. Such reminders are important because scheduled monitoring often occur infrequently, for example, at three or six month intervals.
Following the reminder, the patient must locate the equipment some time prior to the actual start of the scheduled monitoring. After connecting or applying the ECG electrodes, the patient must connect them to the monitoring device. If the monitoring device is a transtelephonic device, that device must also be plugged into a wall socket. The patient waits for the call from the nurse/technician and then begins to transmit the ECG, when instructed to do so. If the ECG electrodes do not have adequate contact with the skin or improperly positioned, the patient is instructed to reposition the ECG electrodes to try another transmission. The nurse/technician on the other end of the line can only hope the patient will reposition the electrodes properly. At times, many attempts are made without much success. In such cases, the only option is to schedule a clinic visit to ensure the acquisition of a diagnostic quality ECG tracing.
The present invention, inter alia, overcomes the various limitations of the prior art and simplifies the steps required to collect reliable medical data. Specifically, the present invention includes a cable onto which are attached two or three objects, at least two of which are hand-holdable structures that the patient grasps in the hand in addition to any optional lightweight RF telemetry head. The holdable structure incorporates ECG electrodes. These electrodes ensure good skin-electrode contact to detect cardiac depolarizations. The RF telemetry head is implemented to detect ECGs via electrodes and also downlink with an IMD if needed. When arranged in this manner, the RF telemetry head serves a dual role by detecting ECGs and/or collecting and transmitting data from the IMD. Specifically, when the telemetry head is used to detect depolarization potentials, surface ECG electrodes are incorporated into the telemetry head are used. In the alternative, the head could be used to collect data from the IMD, while simultaneous collecting depolarization data via the electrodes.
In another embodiment, the lightweight telemetry head may be used solely as a means of collecting IMD data. Generally, the head may collect continuous data from the holdable structures or stored data from the IMD. Preferably, a shielded cable RF/telemetry unit connects the holdable structures to the telemetry head. The RF/telemetry unit transmits ECGs and/or collected IMD data via any one of several means, hard-wired, RF telemetry, infra-red connectivity, BlueTooth or Home RF technology, transtelephonic, or other standard connector known in the art. The RF telemetry of the present invention is similar to telemetry systems disclosed in commonly assigned U.S. Pat. No. 6,167,310 to Grevious; U.S. Pat. No. 5,752,977 to Grevious et al. and U.S. Pat. No. 5,350,411 to Ryan et al. which patents are incorporated herein by reference in their entirety.
Because of the relatively advanced age of the average IMD patients, it is preferred to offer a system that takes into account the potential for some disability (e.g., arthritis) in addition to being user friendly. The present invention addresses such issues. Further, the present invention the use of gels by incorporating ECG electrodes in the holdable structure and/or telemetry head. These electrodes require only dry skin contact.
The present invention implements a hand holdable structure that allows an easy, natural grip to enable patients to apply a simple gentle grip on the structure to record ECGs. There is no need to use a band or other means to ensure a tight or forced grip. The design takes into account the possibility that an individual patient might have an impaired grip and may be unable to exert to a tight grip around the structure. The total weight of the structure and associated cable(s) and devices have been kept very light. Preferably, the cable weighs less than 2 pounds, to accommodate those patients who find it difficult to lift and support heavy weights.
Collection of ECG tracings automatically begins when the patient grasps the structure and the lightweight telemetry head maintains a good skin-electrode contact. When the telemetry head is in use to collect medical device data, grasping the structure with good skin-electrode contact automatically activates both ECG acquisition and data collection. Subsequently, as soon as the patient breaks skin-electrode contact, ECG acquisition and is terminated.